Stromal transdifferentiation drives lymph node lipomatosis and induces extensive vascular remodeling

Abstract

Lymph node (LN) lipomatosis is a common, but rarely discussed phenomenon, associated with aging, involving a gradual exchange of the LN parenchyma into adipose tissue. The mechanisms behind these changes and the effects on the LN have been unknown. We show that LN lipomatosis starts in the medullary regions of the human LN and link the initiation of lipomatosis to transdifferentiation of LN medullary fibroblasts into adipocytes. The latter is associated with a downregulation of lymphotoxin beta expression. We also show that medullary fibroblasts, in contrast to the reticular cells in the T-cell zone, display an inherent higher sensitivity for adipogenesis. Progression of lipomatosis leads to a gradual loss of the medullary lymphatic network, but at later stages, collecting-like lymphatic vessels, are found inside the adipose tissue. The stromal dysregulation includes a dramatic remodeling and dilation of the high endothelial venules associated with reduced density of naive T-cells. Abnormal clustering of plasma cells is also observed. Thus, LN lipomatosis causes widespread stromal dysfunction with consequences for the immune contexture of the human LN. Our data warrant an increased awareness of LN lipomatosis as a factor contributing to decreased immune functions in the elderly and in disease.

Lymph node lymphatic endothelial cells as multifaceted gatekeepers in the immune system

“…The inflammation-induced increase in LN LEC proliferation coincides with type 1 interferon-induced PD-L1 overexpression on human and mouse LECs [76], although the mechanistic relevance of this association remains to be studied. Of note, other disease processes such as age-dependent accumulation of adipocytes in human LNs might cause marked loss of medullary sinus LECs and their replacement by collecting lymphatic vessels [77]; indeed, the functional consequences of such events and their disease-specific contexts remain currently unknown.…”